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Register a new userMeasurements of the branching fractions of the semileptonic decays $Xi_{c}^{0} to Xi^{-} ell^{+} u_{ell}$ and the asymmetry parameter of $Xi_{c}^{0} to Xi^{-} pi^{+}$
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Using data samples of 89.5 and 711 fb$^{-1}$ recorded at energies of $sqrt{s}=10.52$ and $10.58$ GeV, respectively, with the Belle detector at the KEKB $e^+e^-$ collider, we report measurements of branching fractions of semileptonic decays $Xi_{c}^{0} to Xi^{-} ell^{+} u_{ell}$ ($ell=e$ or $mu$) and the $CP$-asymmetry parameter of $Xi_{c}^{0} to Xi^{-} pi^{+}$ decay. The branching fractions are measured to be ${cal B}(Xi_{c}^{0} to Xi^{-} e^{+} u_{e})=(1.31 pm 0.04 pm 0.07 pm 0.38)%$ and ${cal B}(Xi_{c}^{0} to Xi^{-} mu^{+} u_{mu})=(1.27 pm 0.06 pm 0.10 pm 0.37)%$, and the decay parameter $alpha_{Xipi}$ is measured to be $0.63 pm 0.03 pm 0.01$ with much improved precision compared to the current world average. The corresponding ratio ${cal B}(Xi_{c}^{0} to Xi^{-} e^{+} u_{e})/{cal B}(Xi_{c}^{0} to Xi^{-} mu^{+} u_{mu})$ is $1.03 pm 0.05pm 0.07$, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ${cal A}_{CP} = (alpha_{Xi^{-}pi^{+}} + alpha_{bar{Xi}^{+}pi^{-}})/(alpha_{Xi^{-}pi^{+}} - alpha_{bar{Xi}^{+}pi^{-}}) = 0.024 pm 0.052 pm 0.014$ is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the $Xi_{c}^{0} to Xi^{-} pi^+$ branching fraction.
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Using the data sample of 711 fb$^{-1}$ of $Upsilon(4S)$ on-resonance data taken by the Belle detector at the KEKB asymmetric-energy electron-positron collider, we present the first measurements of branching fractions of the decays $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{0}$, $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0}$, and $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0} $. The signal yields for these decays are extracted from the recoil mass spectrum of the system recoiling against $bar{Lambda}_{c}^{-}$ baryons in selected $B^-$ candidates. The branching fraction of $B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2790)^{0}$ is measured to be $ (1.1 pm 0.4 pm 0.2)times 10^{-3}$, where the first uncertainty is statistical and the second systematic. The 90% credibility level upper limits on ${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}^{0})$ and ${cal B}(B^{-} to bar{Lambda}_{c}^{-} Xi_{c}(2645)^{0})$ are determined to be $6.5times 10^{-4}$ and $7.9times 10^{-4}$, respectively.
Using the entire data sample of $980$ $fb^{-1}$ integrated luminosity collected with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider, we present an amplitude analysis measuring the branching fractions of the Cabibbo-allowed, $W$-exchange resonant decay $Xi_{c}^{0} rightarrow Xi^{0} phi (to K^+ K^-)$ with a polarized $phi$ and the non-resonant decay via a direct process $Xi_{c}^{0} rightarrow Xi^{0} K^+ K^-$. We present these measurements, relative to the normalization mode $Xi^{-}pi^{+}$, and find branching ratios $frac{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{0} phi (rightarrow K^{+}K^{-}))}{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{-} pi^{+})} = 0.036 pm 0.004 (stat.) pm 0.002 (syst.)$ and $frac{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{0} K^{+} K^{-})}{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{-} pi^{+})} = 0.039 pm 0.004 (stat.) pm 0.002 (syst.)$ which suggest that only minor cusping peaks occur in the combinatorial background of $Omega^{*-} to Xi^{0}K^{-}$ due to these $Xi_{c}^{0}$ decays.
Using a data sample of 980 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we study the processes of $Xi^0_cto Lambdabar K^{*0}$, $Xi^0_cto Sigma^0bar K^{*0}$, and $Xi^0_cto Sigma^+K^{*-}$ for the first time. The relative branching ratios to the normalization mode of $Xi^0_ctoXi^-pi^+$ are measured to be $${cal B}(Xi^0_cto Lambdabar K^{*0})/{cal B}(xicto Xi^-pi^+)=0.18pm0.02({rm stat.})pm0.01({rm syst.}),$$ $${cal B}(Xi^0_cto Sigma^0bar K^{*0})/{cal B}(xicto Xi^-pi^+)=0.69pm0.03({rm stat.})pm0.03({rm syst.}),$$ $${cal B}(Xi^0_cto Sigma^+K^{*-})/{cal B}(xicto Xi^-pi^+)=0.34pm0.06({rm stat.})pm0.02({rm syst.}),$$ where the uncertainties are statistical and systematic, respectively. We obtain %measure the branching fractions of $Xi^0_cto Lambdabar K^{*0}$, $Xi^0_cto Sigma^0bar K^{*0}$, and $Xi^0_cto Sigma^+K^{*-}$ to be $${cal B}(Xi^0_cto Lambdabar K^{*0})=(3.3pm0.3({rm stat.})pm0.2({rm syst.})pm1.0({rm ref.}))times10^{-3},$$ $${cal B}(Xi^0_cto Sigma^0bar K^{*0})=(12.4pm0.5({rm stat.})pm0.5({rm syst.})pm3.6({rm ref.}))times10^{-3},$$ $${cal B}(Xi^0_cto Sigma^+K^{*-})=(6.1pm1.0({rm stat.})pm0.4({rm syst.})pm1.8({rm ref.}))times10^{-3},$$ where the uncertainties are statistical, systematic, and from ${cal B}(xic to Xi^-pi^+)$, respectively. The asymmetry parameters $alpha(Xi^0_cto Lambdabar K^{*0})$ and $alpha(Xi^0_cto Sigma^+K^{*-})$ are $0.15pm0.22({rm stat.})pm0.04({rm syst.})$ and $-0.52pm0.30({rm stat.})pm0.02({rm syst.})$, respectively, where the uncertainties are statistical followed by systematic.
The first measurements of differential branching fractions of inclusive semileptonic ${B to X_u , ell^+, u_{ell}}$ decays are performed using the full Belle data set of 711 fb$^{-1}$ of integrated luminosity at the $Upsilon(4S)$ resonance and for $ell = e, mu$. Differential branching fractions are reported as a function of the lepton momentum, the four-momentum-transfer squared, light-cone momenta, the hadronic mass, and the hadronic mass squared. They are obtained by subtracting the backgrounds from semileptonic ${B to X_c , ell^+, u_{ell}}$ decays and other processes, and corrected for resolution and acceptance effects. The measured distributions are compared to predictions from inclusive and hybrid ${B to X_u , ell^+, u_{ell}}$ calculations.
We present measurements of partial branching fractions of inclusive semileptonic $B to X_u , ell^+, u_{ell}$ decays using the full Belle data set of 711 fb$^{-1}$ of integrated luminosity at the $Upsilon(4S)$ resonance and for $ell = e, mu$. Inclusive semileptonic $B to X_u , ell^+, u_{ell}$ decays are CKM suppressed and measurements are complicated by the large background from CKM-favored $B to X_c , ell^+, u_{ell}$ transitions, which have a similar signature. Using machine learning techniques, we reduce this and other backgrounds effectively, whilst retaining access to a large fraction of the $B to X_u , ell^+, u_{ell}$ phase space and high signal efficiency. We measure partial branching fractions in three phase-space regions covering about $31%$ to $86%$ of the accessible $B to X_u , ell^+, u_{ell}$ phase space. The most inclusive measurement corresponds to the phase space with lepton energies of $E_ell^B > 1 $ GeV, and we obtain $Delta mathcal{B}(B to X_u ell^+ , u_ell) = left( 1.59 pm 0.07 pm 0.16 right) times 10^{-3}$ from a two-dimensional fit of the hadronic mass spectrum and the four-momentum-transfer squared distribution, with the uncertainties denoting the statistical and systematic error. We find $left| V_{ub} right| = left( 4.10 pm 0.09 pm 0.22 pm 0.15 right) times 10^{-3}$ from an average of four calculations for the partial decay rate with the third uncertainty denoting the average theory error. This value is higher but compatible with the determination from exclusive semileptonic decays within 1.3 standard deviations. In addition, we report charmless inclusive partial branching fractions separately for $B^+$ and $B^0$ mesons as well as for electron and muon final states. No isospin breaking or lepton flavor universality violating effects are observed.
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